File reading/writing question

After a disasterous last attempt at programming, I tried my hand at something a little easyer! Namely... Encryption! I'm quite pleased with my current handy-work... but there's something that I don't quite understand.

The following program (and it's Decrypting counterpart) work fine on .txt and .bmp files... but for some odd reason it mangles .jpg, .exe, .doc and a bunch of other file formats.

Code:

---

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

int main ()
{

/*        The following variables are (in order of apearance):
        Object for File Input || Object for File Output || Variable to hold the Input Filename ||
        Variable to hold the Output Filename || Variable for the Current Character || Variable to
        put the Encrypted character in || Integer to put the characters ASCII value || Boolean that states
        wheter this is the first cycle or not || Integer holding the file size
*/
        ifstream Fileop;
        ofstream DestFil;
        char Filenam[32];
        char OutFile[32];
        char c;
        char e;
        string ch;
        int asc;
        bool firstrun = true;
        long begin,end;

        cout << "Encryptor\n-----------\nCreated by:Rider Rockon";        // A little bit of interface

        cout << "\n\n\nFile to Encrypt:> ";       
        cin >> Filenam;                                // Wait for input, make Filenam whatever was typed
        cout << "Destination File:> ";
        cin >> OutFile;                                // Wait for input, make OutFile whatever was typed

cout << "\n Opening Input: " << Filenam << " and Output: " << OutFile << "\n";

        Fileop.open (Filenam);
        DestFil.open(OutFile,ios::trunc);

        // Count File size & Return the cursor to the start of the file
        begin = Fileop.tellg();
        Fileop.seekg (0, ios::end);
        end = Fileop.tellg();
        Fileop.seekg (0, ios::beg);

        cout << "Encrypting " << (end-begin) << " bytes of Data...\n";

        while (Fileop.good())        // As long as there's no Error or End of File
          {

                ch = "";

                if ( firstrun == false )
                  {
                        // This is where the Encrypting takes place, when done, put it in ch
                        asc = asc + 1; ch = asc;
       
                        // Write ch to the file
                        DestFil <<  ch;
                  }
                else
                  { firstrun = false; }
               
                c = Fileop.get();        // Get the next character in the Input file, put it in c
                asc = c;                // asc now contains the ASCII value of c
          };

cout << "\nDone...\n";
Fileop.close();
DestFil.close();
  return 0;
}

---

I'm still sort of new to all of this and I'm not really sure where the problem is...

I'd really appreciate any help regarding the subject :)

Code:

---

#include <iostream>
#include <fstream>
using namespace std;

int main( int argc, char* argv[] )
{
        int m;
        ifstream MyInFile (argv[1], ios::in | ios::binary);
        ofstream MyOutFile (argv[2], ios::out | ios::binary);
        while (MyInFile.good())
        {
                MyInFile.read(reinterpret_cast < char * > (&m), sizeof(m));
                ++m;
                MyOutFile.write(reinterpret_cast < char * > (&m), sizeof(m));
        }
        MyInFile.close();
        MyOutFile.close();
        return 0;
}

---

Why is this in the C# forum? This is C++.

So it is. Moved.

Quote:

---

Originally Posted by BobS0327

Code:

---

#include <iostream>
#include <fstream>
using namespace std;
 
int main( int argc, char* argv[] )
{
    int m;
    ifstream MyInFile (argv[1], ios::in | ios::binary);
    ofstream MyOutFile (argv[2], ios::out | ios::binary);
    while (MyInFile.good())
    {
        MyInFile.read(reinterpret_cast < char * > (&m), sizeof(m));
        ++m;
        MyOutFile.write(reinterpret_cast < char * > (&m), sizeof(m));
    }
    MyInFile.close();
    MyOutFile.close();
    return 0;
}

---

---

I'm not quite sure what you're proposing here... I'm still quite new at C++

The read loop is what confuses me the most... could you elaborate?

Quote:

---

Why is this in the C# forum? This is C++.

---

Whoops, my bad.

The default file type is non binary or "text". Text files get their newlines converted to CR-LF pairs on write and
vice versa on read; reading in "text" mode stops at the first ^Z character. Reading binary files as text will
therefore corrupt the data and fail to read all the data you need. To avoid this, you must call the constructor
with an explicit ios::binary parameter and use the appropriate functions.

File streams include two member functions specifically designed to input and output binary data
sequentially: write and read. The first one (write) is a member function of ostream
inherited by ofstream. And read is a member function of istream that is inherited by ifstream.

Although the read and write methods accept a char* pointer, there is no requirement that the data you read
and/or write be held in a char array. You can read or write any type of data including complex data objects
using simple type casting of pointers.

In binary files, to input and output data with the extraction and insertion operators (<< and >>)
is not efficient, since we do not need to format any data, and data may not use the separation codes
used by text files to separate elements (like space, newline, etc...).

Finally, you can place your encryption/decryption routine between the read and write functions, where the ++m
statement is located. I just used the ++m statement to test the code before posting it. It is not relevant
for your use and can be deleted.

Thanks for the help so far! I really appreciate it!

Just to try out your code bit, I made a small program that simply opens a file, and copies it to another file, character by character.

It seems like all the file types get converted appropriatly! But it does something odd with a small txt file I tried... it appends "in" to the end... would you have any idea where this might come from?

I more or less copied your example code... (removing the ++m because it was causing strange corruptions for some reason...)

Again, any help would be greatly appreciated :)

sizeof int is 4 (on 32 bit systems) so the sample reads and writes 4 bytes at once (or more on some systems)

You should read and write 1 byte at once,
use unsigned char for storing it.

> sizeof int is 4 (on 32 bit systems)
And sizeof(int) is 1 on other 32 bit systems.

But most newbies are not likely to come across such DSP devices when they're starting.

I'm not sure I"m following...

does this mean I should declare the char pointer as an unsigned char? Or should I declare the integer m (as the example states) as unsigned?

And in the case of the former, how do I do this? I'm not very knowledgeable in the field of pointers just yet... I declared this pointer as BobS0327's example stated... in the int main ()...

declare m as unsigned char

Allright! That got rid of the thing... there's only 1 thing wrong now... at the end of a text file, it appends the last character twice.

I'm sorry to be such a bother, I'm not quite "at home" in C++ just yet :)

Quote:

---

Originally Posted by Rider

Allright! That got rid of the thing... there's only 1 thing wrong now... at the end of a text file, it appends the last character twice.

I'm sorry to be such a bother, I'm not quite "at home" in C++ just yet :)

---

It is because the stream test is done before read, not after, so even when the read failed - it still writes the character to the output

Ah! Excellent! That solves everything!

Now I have another question:

In my original program I converted the char read to an integer (it's ASCII value), did some math with that integer and put it back...

I've tried a few things, but I can't seem to get the value from char (the pointer) into the integer anymore... and I don't really know how I define the write procedure to... for example... write the string CH (wich is now encrypted) to the new file.

also... what is EXACTLY going on in the read/write procedure? Would you be so kind as to break down what is going on?

Maybe you should read http://www.cprogramming.com/tutorial/cfileio.html this
and http://www.cprogramming.com/tutorial/c/lesson11.html this

Allright, after a bit of messing around with the code (and your second link, vart) I've come to create the following:

Code:

---

while (Fileop.good())        // As long as there's no Error or End of File
          {

                if ( firstrun == false ) { DestFil.write(reinterpret_cast < char * > (&och), sizeof(och)); };

                Fileop.read(reinterpret_cast < char * > (&ich), sizeof(ich));
                asc = (int)ich;

                        // Encrypt ASC here preparing it for output
                        asc = asc + 1;
                och = (unsigned char)asc;

                if ( firstrun == true ) { firstrun = false; };

          };

---

(Asc is an INT, ich and och both Unsigned CHAR's, firstrun is a boolean)

But something goes wrong, because the file being encrypted is reduced in size greatly (My 413KB file became 3.50KB) and I can't quite figure out where I'm messing up.

My guess would be that something gets 'lost in translation' while being converted back and forth from char to int to char again, but like I said, I don't know exactly what's going awry here.

Any help on the matter is greatly appreciated :)

where ich and och are defined?

They're defined above that, I didn't think it'd be that important, but regardless, this is where they are defined:

Code:

---

        ifstream Fileop;
        ofstream DestFil;
        char Filenam[32];
        char OutFile[32];
        unsigned char ich;
        unsigned char och;
        int asc;
        bool firstrun = true;
        long begin,end;

---

1. you can remove reinterpreter cast
2. you can remove ; after }
3. you should check the number of bytes written by the write function, if it is 0 - you should check what charaster cause this
4. have you tried to write the file without changing value? it is working as should?

Regarding 1, I'm not quite sure what the right way would be to go about that, just removing it b0rks the code :)

on 3, I made the program output the size of every character read, and already it's coming up short on bytes...

4. I've done the following:

Just reading and writing without converting the values to another type of variable (basically the example provided by BobS0327) and it works fine, the entire file is duplicated.

Reading and writing without changing the value, but WITH converting it from the read procedure through all the variables, and back to the write procedure. This didn't work.

*Bump*

I'd really like some help on this issue... my current Encryption program looks like this:

Code:

---

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

int main (char*)
{


        ifstream Fileop;
        ofstream DestFil;
        char Filenam[32];
        char OutFile[32];
        unsigned char ich;
        unsigned char och;
        int asc;
        bool firstrun = true;
        long begin,end;

        cout << "Encryptor\n-----------\nCreated by:Rider Rockon";        // A little bit of interface

        cout << "\n\n\nFile to Encrypt:> ";       
        cin >> Filenam;                                // Wait for input, make Filenam whatever was typed
        cout << "Destination File:> ";
        cin >> OutFile;                                // Wait for input, make OutFile whatever was typed

cout << "\n Opening Input: " << Filenam << " and Output: " << OutFile << "\n";

        Fileop.open (Filenam);
        DestFil.open(OutFile,ios::trunc);

        // Count File size & Return the cursor to the start of the file
        begin = Fileop.tellg();
        Fileop.seekg (0, ios::end);
        end = Fileop.tellg();
        Fileop.seekg (0, ios::beg);

        cout << "Encrypting " << (end-begin) << " bytes of Data...\n";

        while (Fileop.good())        // As long as there's no Error or End of File
          {

                if ( firstrun == false ) { DestFil.write(reinterpret_cast < char * > (&och), sizeof(och)); };

                Fileop.read(reinterpret_cast < char * > (&ich), sizeof(ich));
                asc = (int)ich;

                        // Encrypt ASC here preparing it for output
                        asc = asc + 1;
                och = (unsigned char)asc;

                if ( firstrun == true ) { firstrun = false; };

          };

cout << "\nDone...\n";

Fileop.close();
DestFil.close();
  return 0;
}

---

as stated above, the file being encrypted is reduced in size greatly (My 413KB file became 3.50KB) and I can't quite figure out where I'm messing up.

Could anyone please help me out? I'm just a beginning programmer and I haven't got too much experience so far... heck... I'm suprised I even got this far!

Any help on the matter would be greatly appreciated :)

hmmm...
Have you tried the suggestion of the BobS0327?

Code:

---

ifstream MyInFile (argv[1], ios::in | ios::binary);
ofstream MyOutFile (argv[2], ios::out | ios::binary);

---

Code:

---

int main (char*)

---

Is this legal?

No, most definitely not.

The first step in writing any file transformation program is to simply write something which copies the input to the output without changing it at all. Until you can manage that, the rest of the problem doesn't matter.

Code:

---

#include<iostream>
#include<fstream>
using namespace std;

int main()
{
    ifstream Fileop ( "a.exe", ios::in | ios::binary );
    ofstream DestFil( "copy.bin", ios::out | ios::binary );
    char ch;

    while ( Fileop.get(ch) ) {
        DestFil.put(ch);
    }

    Fileop.close();
    DestFil.close();

    return 0;
}


$ # copying itself
$ ls -l a.exe ; ./a.exe ; ls -l copy.bin ; cmp a.exe copy.bin
-rwxr-xr-x 1 who None 477334 Dec 22 17:34 a.exe
-rw-r--r-- 1 who None 477334 Dec 22 17:35 copy.bin

---

Yes well, I already accomplished that earlyer. The only problem is that my method of encryption (by recalculating the ASCII value of the read character) requires the character to be moved through other variables... somewhere in that particular process, something goes wrong.

This routine:

Code:

---

while (Fileop.good())        // As long as there's no Error or End of File
          {

                if ( firstrun == false ) { DestFil.write(reinterpret_cast < char * > (&och), sizeof(och)); };

                Fileop.read(reinterpret_cast < char * > (&ich), sizeof(ich));
        //        asc = (int)ich;

Fileop.read(reinterpret_cast < char * > (&pos), sizeof(pos));

                        // Encrypt ASC here preparing it for output
        //                asc = asc + 1;
        //        och = (unsigned char)asc;

                if ( firstrun == true ) { firstrun = false; };

          };

---

This was the original routine, kudos to BobS0327, and it worked fine... But I'll try your version Salem... it looks a lot more compact at least (and, for a coding newb like me, a lot more clear on what it does :D)

Well it's really rather simple,

From this

Code:

---

    while ( Fileop.get(ch) ) {
        DestFil.put(ch);
    }

---

To this

Code:

---

    while ( Fileop.get(ch) ) {
        ch = myEncrypt(ch);
        DestFil.put(ch);
    }

---

Before messing with files, you can test the function with very basic tests like

Code:

---

int main ( ) {
    cout << myEncrypt('A');
    // or
    for ( int i = 'A' ; i <= 'Z' ; i++ ) cout << myEncrypt( i );
}

---

When both ideas are working well separately, then you can try bringing them together.

It doesn't hurt to have a couple of 'test' projects on the side containing just a main(), where you can work on a specific idea in isolation. When you've got it working, then simply copy/paste what you want to the real project.